Hip implant with porous body

ABSTRACT

A hip implant having two distinct bodies, a neck body and a bone fixation body. The neck body is formed from a solid metal and has an interface for connecting to a femoral ball. The bone fixation body has an elongated shape and is formed as a porous structure that is inserted into an intramedullary canal of a patient.

FIELD OF THE INVENTION

[0001] The disclosure herein generally relates to hip implants forosseointegration into bone and, more particularly, to hip implantshaving a porous body.

BACKGROUND OF THE INVENTION

[0002] Much effort has been directed to integrating hip implants intosurrounding bone. Ideally, a hip implant would be placed into the femur,and thereafter bone would readily grow into the surface of the implant.To achieve this objective, many different surface technologies have beenapplied to hip implants. In some instances, the surface of the implantis roughened, grit-blasted, plasma-sprayed, or microtextured. In otherinstances, the surface is coated with a biological agent, such ashydroxylapatite (known as HA). In all of these instances, the goal isthe same: Produce a surface on the hip implant into which surroundingbone will grow or bond.

[0003] Porous coatings have also been applied to surfaces of hipimplants. These coatings are advantageous since bone will indeed growinto a portion of the outer most surface of the implant.Osseointegration, to a limited extent then, has been achieved withporous coated surfaces. These surfaces though are far from ideal interms of accepting and encouraging bone growth into the body of theimplant.

[0004] As one disadvantage, porous surfaces are often thin coatingsapplied to the metallic substrate of the implant. Bone surrounding theimplant can only grow into the thin coating itself. Bone cannot growthrough the coating and into the metallic substrate. The depth of bonegrowth into the implant is limited to the depth of the porous coating.Bone simply cannot grow completely through the implant or deeply intothe body of the implant.

[0005] It therefore would be desirable to have a hip implant that offersoptimum anchoring in bone with bone growth into a porous body.

SUMMARY OF THE INVENTION

[0006] The present invention is directed toward a femoral hip implantfor integrating with surrounding bone. In one exemplary embodiment, theimplant includes two separate and distinct bodies, a neck body and abone fixation body. Together, these bodies form a complete femoral hipimplant.

[0007] The neck body is located at the proximal end of the implant andincludes an interface adapted to connect with a femoral ball component.In an exemplary embodiment, this interface comprises an elongatedcylindrical shaft or neck adapted to matingly engage with a cylindricalrecess in the femoral ball component.

[0008] In one exemplary embodiment, the neck body is formed of a solidmetal piece, such as titanium, titanium alloy, or other metals or alloyssuitable for a hip prosthesis. The body is formed from a machiningprocess and has a base portion that may comprise a collar. The neckextends outwardly away from the base portion.

[0009] The bone fixation body is formed of a porous metal, such astitanium or other metals or alloys suitable for a hip prosthesis. In oneexemplary embodiment, the body is formed with a sintering process, iscompletely porous, and does not include a metal substrate. In crosssection then, the body has a porous structure with no solid metalsubstrate.

[0010] The neck body (formed of solid metal) and the bone fixation body(formed of a completely porous structure) are permanently connectedtogether. When connected, the two bodies form a hip implant. In oneexemplary embodiment, these two bodies are connected with a sinteringprocess.

[0011] In one exemplary embodiment, the bone fixation body portion ofthe hip implant is completely porous. This porous structure extendsentirely through the body of the implant along the region where theimplant engages femoral bone. As such, the depth of bone growth into theimplant is not restricted to a thin porous coating. Instead, bone cangrow deeply into the body of the implant or completely into and eventhrough the body of the implant. The implant, then, can become fullyintegrated into surrounding bone with the structure of bone dispersedthroughout the body of the implant.

[0012] In one exemplary embodiment, the geometric structure of theporous body may be shaped and sized to emulate the shape and size ofnatural bone surrounding the implant. Specifically, the porous structureof the bone fixation body thus replicates the porous structure ofnatural bone itself. The porous structure, thus, readily accepts andencourages surrounding bone to grow into and even through the body ofthe implant.

[0013] In one exemplary embodiment, the bone fixation body may be dopedwith bone growth agents to enhance and stimulate bone growth. Theseagents can be placed throughout the bone fixation body so bone growsdeeply into the implant or completely through the implant. Bone growth,as such, is not restricted to the surface of the implant.

[0014] As noted, the porous structure of the implant enables bone togrow deeply into or completely through the implant itself. Growth deepinto the body of the implant provides an extremely strong interfacebetween the implant and surrounding natural bone. As such, thelikelihood that the implant will loosen is greatly reduced. Further, theoverall long-term acceptance of the implant in the bone is increased.Further yet, the porous structure of the bone fixation body reduces theoverall weight of the hip implant.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a side view of one embodiment of a hip implant of anexemplary embodiment of the present invention.

[0016]FIG. 2 is a cross-sectional view of the implant of FIG. 1 embeddedin the intramedullary canal of a femur.

[0017]FIG. 3 is a side view of another exemplary embodiment of a hipimplant of the present invention.

[0018]FIG. 4 is a cross-sectional view of FIG. 3 showing the hip implantembedded in the intramedullary canal of a femur.

[0019]FIG. 5 is a side cross-sectional view of yet another exemplaryembodiment of a hip implant of the present invention.

[0020]FIG. 6 is a side view of yet another exemplary embodiment of thepresent invention.

[0021]FIG. 7 is a top view of a horizontal cross section of an exemplaryembodiment of the present invention.

[0022]FIG. 8 is a top view of a horizontal cross section of anotherexemplary embodiment of the present invention.

[0023]FIG. 9 is a top view of a horizontal cross section of yet anotherexemplary embodiment of the present invention.

DETAILED DESCRIPTION

[0024] Referring to FIGS. 1 and 2, a hip implant 10 is shown accordingto an exemplary embodiment of the invention. Implant 10 is preferablyconstructed of a biocompatible material such as titanium, titaniumalloy, or other metals or alloys suitable for a hip prosthesis. Implant10 comprises two primary components or bodies, a neck body 14 and a bonefixation body 16.

[0025] The neck body 14 is located at the proximal end 18 of the hipimplant 10 and functions to connect the hip implant 10 to a sphericallyshaped femoral ball 19 and acetabular component (not shown). The neckbody extends from a flat or planar distal end surface 21 to a proximalend surface 23. Further, the neck body has a base portion 20 thatincludes a collar 22 adapted to seat against a resected or end portionof a femur. An interface is adapted to connect the neck body to thefemoral ball. A neck portion 24 extends outwardly from the base portion20. This neck portion has a short cylindrical configuration and has anend 26 with a slight taper. This end 26 is adapted to be received in acorrespondingly shaped and sized cylindrical recess 30 in the femoralball 19. Together, end 26 and recess 30 form a Morse taper connection.

[0026] Preferably, the neck body 14 is formed of a biocompatible metal,such as a solid metal piece of titanium, titanium alloy or other metalsor alloys suitable for a hip prosthesis. The body can be machined tohave a size and shape shown in the figures or other sizes and shapesadapted for use as a hip implant.

[0027] The bone fixation body 16 has an elongated tapering shape thatextends from a flat or planar proximal end surface 40 to a roundeddistal end surface 42. The distal end surface 21 of neck body 14connects or fuses to the proximal end surface 40 of the bone fixationbody 16 at a junction 44.

[0028] In the exemplary embodiments of FIGS. 1 and 2, bone fixation body16 is formed from a porous metal, such as titanium. The body has acompletely porous structure that extends throughout the entire body fromthe proximal end surface 40 to distal end surface 42. Specifically, asshown in FIG. 2, body 16 does not include a solid metal substrate.

[0029]FIG. 2 shows the implant 10 embedded in a femur 50 of a patient.In this embodiment, the implant is embedded into the intramedullarycanal 52 of the femur. The length of the bone fixation body 16 extendsalong the region where the implant contacts surrounding bone. As shown,the collar 22 seats against a resected end 56 of the femur above anentrance 57 to the intramedullary canal 59. In this embodiment, the bonefixation body 16 extends into the intramedullary canal, and the neckbody 14 extends outwardly from the resected end of the initramyedullarycanal and femur. Further, the proximal end surfaced 40 is adjacent theentrance 57 to the intramedullary canal.

[0030] As noted, the bone fixation body 16 has a porous structure thatextends throughout the body from the proximal end surface to the distalend surface. By “porous,” it is meant that the material at and under thesurface is permeated with interconnected interstitial pores thatcommunicate with the surface. The porous structure can be formed bysintering titanium, titanium alloy powder, metal beads, metal wire mesh,or other suitable materials, metals, or alloys known in the art.

[0031] The porous structure of body 16 is adapted for the ingrowth ofcancellous and cortical bone spicules. In the exemplary embodiment, thesize and shape of the porous structure emulates the size and shape ofthe porous structure of natural bone. Preferably, the average porediameter of body 16 is about 40 μm to about 800 μm with a porosity fromabout 45% to 65%. Further, the interconnections between pores can have adiameter larger than 50-60 microns. In short, the geometricconfiguration of the porous structure should encourage natural bone tomigrate and grow into and throughout the entire body 16.

[0032] Although specific ranges are given for pore diameters, porosity,and interconnection diameters, these ranges are exemplary and areapplicable to one exemplary embodiment. In other embodiments, theseranges could be modified, and the resulting hip implant still within thescope of the invention.

[0033] Preferably, body 16 is created with a sintering process. Oneskilled in the art will appreciate that many variations exist forsintering, and some of these variations may be used to fabricate thepresent invention. In the exemplary embodiment, the neck body is formedfrom a solid piece of metal and prepared using conventional and knownmachining techniques. Next, a ceramic mold is provided. The mold has afirst cavity that is sized and shaped to match the size and shape of thebone fixation body. In this first cavity, the sintering material can beplaced. The mold also has a second cavity that is adjacent and connectedto the first cavity. This second cavity is sized and shaped to receivethe neck body. The neck body is positioned in the second cavity suchthat the distal end surface is adjacent and continuous with the firstcavity.

[0034] The sintering material is then placed into the first cavity. Thismaterial may be a titanium alloy powder, such as Ti-6Al-4V. Sonie ofthis powder will contact the distal end surface of the neck body. Themold is then heated to perform the sintering process. During thisprocess, as the material in the first cavity heats and sinters, the bonefixation body forms and simultaneously bonds or fuses to the distal endsurface of the neck body.

[0035] The size and shape of the pores and porous structure produced inthe first cavity depend on many factors, These factors include, forexample, the temperature obtained in the furnace, the sintering time,the size and shape of sintering material, the composition of thesintering material, and the type of ceramic mold used. These factors(and others) can be varied to produce a bone fixation body in accordancewith the present invention. Further, these factors (and others) can bevaried to produce a strong bond between the bone fixation body and neckbody.

[0036] Once the sintering process is finished, the neck body is directlyfused to the bone fixation body. These two bodies are now permanentlyconnected together to form the hip implant.

[0037] In the aforementioned sintering process, the bone fixation bodysimultaneously forms and attaches to the neck body. One skilled in theart though will appreciate that each of these bodies can be fabricatedindependently and subsequently connected together. If the bodies aremade separately, then they may be attached or fused together using knownwelding or brazing techniques, for example.

[0038] In FIG. 1, for example, the bone fixation body has an elongatedtapering body with a slight bow. The bone fixation body, though, mayhave other configurations and still be within the scope of theinvention. The size and shape of the body depend on the size and shapeof the cavity of the mold during the sintering process. This cavity canbe shaped, for example, to emulate the natural size, shape, and contourof a human intramedullary canal. As such, the bone fixation body willmore naturally fit into the intramedullary canal and conform to thenatural anatomical contours of a human patient.

[0039]FIGS. 3 and 4 show another hip implant 50 according to anexemplary embodiment of the invention. With some differences, implant 50is similarly configured to the implant 10. As one difference, the neckbody 60 of implant 50 has two different and distinct regions on itsouter surface. A first region 62 has a smooth outer surface. A secondregion 64 has a bone-engaging surface that is contiguous and adjacent tothe first region 62 on one side and contiguous and adjacent the porousbone fixation body 66 on the other side. The second region is non-porousand is shaped as a band that extends completely around the neck body.This second region can be formed on the outer surface of the neck bodywith various techniques. These techniques include, for example, coatingwith HA, grit-blasting, etching, micro-texturing, other non-poroussurface treatments, or combinations of these techniques. This surface 64is provided as an intermediate zone between the porous body and thesmooth first region 62.

[0040] As shown in FIG. 4, the second region 64 is below collar 68 andis positioned into the intramedullary canal to contact bone. Region 64,then, contacts bone, and region 62 does not contact bone and extendsabove it.

[0041]FIG. 5 shows another implant 70 according to another exemplaryembodiment of the invention. With some differences, implant 70 issimilarly configured to the implant 10. As one difference, neck body 72includes a male protrusion 74 that extends outward from base portion 76.This protrusion 74 is adapted to extend partially into the bone fixationbody 78 of implant 70.

[0042] The protrusion 74 forms a core for the bone fixation body. Asshown in FIG. 5, this protrusion extends past the proximal end surface80 and into the bone fixation body. The depth of the protrusion into thebone fixation body can be increased or decreased in various embodimentsand still remain within the scope of the invention. For example, theprotrusion can partially extend into the bone fixation body and remainsubstantially near the proximal end surface. Alternatively, theprotrusion can extend farther into the bone fixation body toward thedistal end surface 82. In this latter embodiment, the protrusiongradually tapers as it extends toward the distal end surface.

[0043] The size and shape of the protrusion can also have variousembodiments and still remain within the scope of the invention. Forexample, the protrusion can be cylindrical or polygonal, such asrectangular or square. Other configurations are possible as well; theprotrusion can taper or have longitudinal ribs placed along its outersurface. The size and shape of the protrusion can have variousembodiments to serve various functions. For example, the protrusion canbe sized and shaped to provide a strong connection between the neck bodyand bone fixation body. The protrusion can be sized and shaped toprovide an anti-rotational interface between the neck body and bonefixation body. Further, the protrusion can be sized and shaped toprovide additional strength to the bone fixation body or more equally orefficiently distribute loads from the neck body to the bone fixationbody. Other factors as well may contribute to the design of theprotrusion.

[0044]FIG. 6 shows another implant 90 according to an exemplaryembodiment of the invention. Implant 90 has a bone fixation body 92 withan outer surface that has a plurality of undulations 94, such as hillsand valleys. These undulations may be provided as tiny ripples or waves.Alternatively, the undulations may be larger and more rolling.Regardless, the undulations are adapted to firmly secure the implantinto the intramedullary canal of the femur after the implant is placedtherein.

[0045] As shown in FIG. 6, the undulations extend along the entirelength of the bone fixation body 92 from the proximal end surface 96 tothe distal end surface 98. In alternative embodiments, the undulationsdo not extend along the entire length of the bone fixation body, butpartially extend along this body.

[0046]FIGS. 7-9 show various longitudinal cross-sectional shapes of thebone fixation body for different exemplary embodiments of the invention.The bone fixation body may have one single longitudinal cross-sectionalshape, or the body may have numerous different longitudinalcross-sectional shapes. FIGS. 7-9 represent examples of some of theseshapes.

[0047]FIG. 7 shows a trapezoidal longitudinal cross-sectional shape.FIG. 8 shows a triangular longitudinal cross-sectional shape. FIG. 9shows an elliptical or oval longitudinal cross-sectional shape.

[0048] The bone fixation body can be adapted to induce bone growthpartially into or entirely through the body. The body, for example, canbe doped with biologically active substances. These substances maycontain pharmaceutical agents to stimulate bone growth all at once or ina timed-release manner. Such biological active substances are known inthe art.

[0049] Although illustrative embodiments have been shown and described,a wide range of modifications, changes, and substitutions iscontemplated in the foregoing disclosure; and some features of theembodiments may be employed without a corresponding use of otherfeatures. Accordingly, it is appropriate that the appended claims beconstrued broadly and in a manner consistent with the scope of theembodiments disclosed herein.

What is claimed is:
 1. A hip implant, comprising: a neck body extendingfrom a distal end to a proximal end, formed of a biocompatible metal,and having an interface at the proximal end that is adapted to connectto a femoral ball; and a bone fixation body extending from a proximalend to a distal end and formed of a completely porous structure from theproximal to distal ends of the bone fixation body, the proximal end ofthe bone fixation body connected to the distal end of the neck body. 2.The hip implant of claim 1 wherein the bone fixation body is entirelyporous, extends below a resected end of a femur of a patient, and isadapted to integrate with the femur of the patient; and wherein the neckbody is non-porous and extends above the resected end of the femur ofthe patient.
 3. The hip implant of claim 2 wherein the bone fixationbody has horizontal cross-sectional triangular shape.
 4. The hip implantof claim 2 wherein the bone fixation body has horizontal cross-sectionalelliptical shape.
 5. The hip implant of claim 2 wherein the bonefixation body has a horizontal cross-sectional trapezoidal shape.
 6. Thehip implant of claim 2 wherein the neck body is formed of a machinedmetal with a solid metallic structure and further comprises a collaradapted to seat against the resected end of the femur; and wherein thedistal end of the neck body terminates at the resected end of the femur.7. The hip implant of claim 6 wherein the bone fixation body issintered, and the neck body is fused to the bone fixation body.
 8. A hipimplant, comprising: a neck body formed of a non-porous biocompatiblemetal having a smooth outer surface and having a neck adapted to connectto a hip component; and a bone fixation body having one end connected tothe neck body and being formed of a completely porous structurethroughout the entire bone fixation body; wherein the bone fixation bodyextends into an intramedullary canal of a femur of a patient, andwherein the neck body extends at least partially above theintramedullary canal.
 9. The hip implant of claim 8 wherein the bonefixation body has an elongated generally tapering shape that extendsfrom a proximal end surface to a distal end surface, and wherein theproximal end surface is adjacent an entrance to the intramedullary canaland the distal end surface is embedded into the intramedullary canal.10. The hip implant of claim 8 wherein the neck body has a maleprotrusion that extends into the bone fixation body.
 11. The hip implantof claim 10 wherein the protrusion has a shape selected from the groupconsisting of cylindrical, rectangular, and square.
 12. The hip implantof claim 8 wherein neck body comprises a non-porous bone-engagingsection between the smooth outer surface and bone fixation body.
 13. Thehip implant of claim 12 wherein the non-porous bone-engaging section isa band having a rough surface texture.
 14. The hip implant of claim 8wherein the neck body is formed of solid metal and the bone fixationbody is formed of sintered metal material.
 15. The hip implant of claim14 wherein the neck body and bone fixation body are fused together. 16.A hip implant, comprising: a neck body formed of a non-porous machinedmetal having a neck adapted to connect to a femoral ball; and a bonefixation body having an elongated shape with one end connected to theneck body and being formed of a completely porous structure throughoutthe entire bone fixation body, wherein the bone fixation body extendsinto an intramedullary canal of a patient.
 17. The hip implant of claim16 wherein the bone fixation body has a cross section formed entirely ofthe porous structure.
 18. The hip implant of claim 17 wherein the neckbody has a cross section formed of a solid biocompatible metal.
 19. Thehip implant of claim 18 wherein the neck body has a protrusion thatextends into the bone fixation body.
 20. The hip implant of claim 16wherein the bone fixation body has a tapering shape with undulationsalong an outer surface.